UnitedHealth Group beats analysts' expectations with first quarter earnings.

The nation's largest health insurer, UnitedHealth Group, beat analysts' expectations with first-quarter earnings driven by growth in its Medicaid and Medicare customer base and stronger revenue from its Optum subsidiary.

The company reported quarterly earnings of $1.41 billion, or $1.46 per share on diluted earnings, compared with $1.1 billion, or $1.10 per share, during the first quarter of 2014. Analysts polled by Thomson Reuters were expecting $1.35 per share.

Total revenues were $35.76 billion for the quarter, up from $31.71 billion during the same months in 2014.

The Optum subsidiary's revenues grew $1.6 billion, or 15 percent, to $12.8 billion for the quarter. Optum includes OptumCare, which manages the health of people for third-party payers such as employers; OptumInsight, which provides health-care software and technology products; and OptumRx, the pharmacy benefits management subsidiary.

The company expects 2015 revenues of $143 billion, an increase of $2 billion from its previous outlook, due to stronger business growth in the first quarter. The company expects earnings to be in the range of $6.15 and $6.30 per share, an increase from the previous outlook of $6 to $6.25 per share.

The company's health insurance subsidiary, UnitedHealthcare, increased its customer base to 45.77 million people as of March 31, up from 44.67 million a year earlier. The company had its greatest growth, on a percentage basis, in government-funded programs, Medicaid and Medicare.

The combined customer base in Medicare Advantage, Medicaid and Medicare Supplement plans was up to 12.18 million people as of March 31 from 10.9 million a year earlier.

The company's commercial membership, which includes insurance sold to workers through employers and government-funded TRICARE coverage for military families and retirees, was 29.4 million at the end of the quarter, up from 29.1 million a year earlier.

Pharmacy benefits managers, or PBMs, help negotiate the prices that customers pay for prescription...

UnitedHealth Group announced at the end of March that it is spending $12.8 billion to acquire Catamaran Corp., a pharmacy benefits manager.

UnitedHealth Group is based in Minnetonka, Minn., and employs about 4,200 people in Connecticut at offices for UnitedHealthcare, Optum, OptumInsight and OptumHealth in Hartford, Rocky Hill, Trumbull and Windsor.

The company's stock closed up 3.65 percent, or $4.28, to $121.60, at the end of trading Thursday.